Acoustic ink printing is a promising direct marking technology because it does not require the nozzles or the small ejection orifices which have been a major cause of the reliability and pixel placement accuracy problems that conventional drop on demand and continuous stream ink jet printers have experienced.
It has been shown that acoustic ink printers have printheads comprising acoustically illuminated spherical focusing lenses can print precisely positioned picture elements (pixels) at resolutions which are sufficient for high quality printing of relatively complex images. See, for example, the copending and commonly assigned U.S. patent applications of Elrod et al, which were filed Dec. 19, 1986 under Ser. Nos. 944,490, 944,698, and 944,701 on "Microlenses for Acoustic Printing", "Acoustic Lens Arrays for Ink Printing" and "Sparse Arrays for Acoustic Printing", respectively. It also has been found that the size of the individual pixels that are printed by such a printer can be varied over a significant range during operation, thereby enabling the printer to impart, for example, a controlled shading to the printed image. See, another copending and commonly assigned U.S. patent application of Elrod et al, which was filed Dec. 19, 1986 under Ser. No. 944,286 on "Variable Spot Size Acoustic Printing".
Although acoustic lens-type droplet ejectors currently are favored, there are other types of droplet ejectors which may be utilized for acoustic ink printing, including (1) piezoelectric shell transducers, such as described in Lovelady et al U.S. Pat. No. 4,308,547, which issued Dec. 29, 1981 on a "Liquid Drop Emitter," and (2) interdigitated transducers (IDT's), such as described in copending and commonly assigned Quate et al U.S. patent application, which was filed Jan. 5, 1987 under Ser. No. 946,682 on "Nozzleless Liquid Droplet Ejectors" now U.S. Pat. No. 4,697,195 as a continuation of application Ser. No. 776,291 filed Sept. 16, 1985 (now abandoned). Furthermore, acoustic ink printing technology is compatible with various printhead configurations; including (1) single ejector embodiments for raster scan printing, (2) matrix configured arrays for matrix printing, and (3) several different types of pagewidth arrays, ranging from (i) single row, sparse arrays for hybrid forms of parallel/serial printing, to (ii) multiple row staggered arrays with individual ejectors for each of the pixel positions or addresses within a pagewidth address field (i. e., single ejector/pixel/line) for ordinary line printing.
For performing acoustic ink printing with any of the aforementioned droplet ejectors, each of the ejectors launches a converging acoustic beam into a pool of ink, with the angular convergence of the beam being selected so that it comes to focus at or near the free surface (i.e., the liquid/air interface) of the pool. Moreover, means are provided for modulating the radiation pressure which each beam exerts against the free surface of the ink. That permits the radiation pressure of each beam to make brief, controlled excursions to a sufficiently high pressure level to overcome the restraining force of surface tension, whereby individual droplets of ink are ejected from the free surface of the ink on command, with sufficient velocity to deposit them on a nearby recording medium.
Hot melt inks have the known advantages of being relatively clean and economical to handle while they are in a solid state and of being easy to liquefy in situ for the printing of high quality images. These advantages could prove to be of substantial value for acoustic ink printing, especially if provision is made for realizing them without significantly complicating the acoustic ink printing process or materially degrading the quality of the images that are printed.